Synergism among BIOLF-62, phosphonoformate, and other antiherpetic compounds

Activity of Penciclovir in Combination with Azido-Thymidine, Ganciclovir, Acyclovir, Foscarnet and Human Interferons against Herpes Simplex Virus Replication in Cell Culture

Combinations of penciclovir (PCV) with other antiviral agents (acyclovir, ACV; ganciclovir, GCV; foscarnet, PFA; azido-thymidine, AZT) or with human interferons (HulFN-α,β,γ) were tested for inhibitory activity against herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2) in cell culture. The antiviral interactions observed between combinations of PCV with ACV or GCV were purely additive. Combinations of PCV with HulFNs demonstrated highly synergistic anti-herpesvirus activity; some synergy was also detected between PCV and PFA against HSV-1. High concentrations of AZT inhibited the antiviral activity of PCV; this antagonism was competitive. In more detailed studies it was demonstrated that high concentrations of AZT also inhibited the antiviral activity of ACV, and that ACV was more sensitive to this antagonism than PCV. It was concluded that the antagonism was unlikely to have clinical significance.

Efficacy of traditional herbal medicines in combination with acyclovir against herpes simplex virus type 1 infection in vitro and in vivo

Traditional herbal medicines have been safely used for the treatment of various human diseases since ancient China. We selected 10 herbal extracts with therapeutic antiherpes simplex virus type 1 (HSV-1) activity. Among these, Geum japonicum Thunb., Rhus javanica L., Syzygium aromaticum (L.) Merr. et Perry, or Terminalia chebula Retzus showed a stronger anti-HSV-1 activity in combination with acyclovir than the other herbal extracts in vitro. When acyclovir and/or a herbal extract were orally administered at doses corresponding to human use, each of the 4 combinations significantly limited the development of skin lesions and/or prolonged the mean survival times of infected mice compared with both acyclovir and the herbal extract alone (P < 0.01 or 0.05). These combinations were not toxic to mice. They reduced virus yields in the brain and skin more strongly than acyclovir alone and exhibited stronger anti-HSV-1 activity in the brain than in the skin, in contrast to acyclovir treatment by itself. Combinations of acyclovir with historically used herbal medicines showed strong combined therapeutic anti-HSV-1 activity in mice, especially reduction of virus yield in the brain.

Potentiating effect of ribavirin on the anti-herpes activity of acyclovir

The combined antiviral effects of acyclovir (ACV) and ribavirin (Rbv) on herpes simplex virus type 1 (HSV-1) and pseudorabies virus (PRV) in cell cultures and on experimental HSV-1 keratitis in rabbits were studied. The antiviral activity in vitro was based on cytopathogenicity inhibition and yield reduction. The combination of the two drugs exhibited synergy as evaluated graphically (isobolograms). Rbv also potentiated the antiviral effect of ACV in vivo, in the experimental HSV-1 keratitis model in rabbits. This was evident from both the severity of corneal lesions and virus shedding in the tear film. The potentiating effect of Rbv on the anti-HSV-1 activity of ACV in vitro was reversed by guanosine.

Synergistic topical therapy by acyclovir and A1110U for herpes simplex virus induced zosteriform rash in mice

Combination therapy with A1110U, an inactivator of the herpes simplex virus (HSV) and the varicella zoster virus ribonucleotide reductase, and acyclovir (ACV) was evaluated for treatment of cutaneous herpetic disease in athymic mice infected on the dorsum. In this model, infection with HSV produces a 'zosteriform-like' rash that is first visible on day 3 or 4 post-infection (p.i.) and eventually extends from the anterior mid-line to the dorsal mid-line of the affected flank. In untreated mice, the infection is fatal at about day 7 p.i. presumably due to central nervous system involvement. Topical treatment of infections induced by either wild-type (wt) HSV-1 or wt HSV-2 with 3% A1110U in combination with 5% ACV resulted in synergistic (P less than 0.01) reductions in lesion scores. Therapy was also synergistic in mice infected with an ACV-resistant thymidine kinase-deficient mutant and an ACV-resistant TK-altered mutant HSV-1 isolated. Combination therapy was very effective in reducing lesion scores of mice infected with an ACV-resistant HSV-1 DNA polymerase mutant, but did not result in statistically significant synergy (P = 0.07) because of the enhanced efficacy of A1110U alone against this virus. These results provide encouragement that the combination of A1110U and ACV may offer an effective therapy for topical treatment of cutaneous HSV infections in humans.

Combined synergistic antiherpetic effect of acyclovir and chlorhexidine in vitro

The combined effect of acyclovir and chlorhexidine on the replication and DNA synthesis of herpes simplex virus was studied. Acyclovir and chlorhexidine showed synergism in the inhibition of the viral replication by enhancing in part the reduction of viral DNA synthesis. These data indicate that combined therapy with acyclovir and chlorhexidine might be beneficial for the control of intraoral herpetic infections.

Ganciclovir. A review of its antiviral activity, pharmacokinetic properties and therapeutic efficacy in cytomegalovirus infections

Ganciclovir is a nucleoside analogue with antiviral activity in vitro against members of the herpes group and some other DNA viruses. It has demonstrated efficacy against human cytomegalovirus infections and should be considered a first-line therapy in the treatment of life- or sight-threatening cytomegalovirus infection in immunocompromised patients. Clinical efficacy varies with the underlying aetiology of immunocompromise and the site of disease, and prompt diagnosis and early treatment initiation appear to improve the response. In patients with cytomegalovirus pneumonia, particularly bone marrow transplant recipients, concomitant administration of cytomegalovirus immune globulin may significantly improve clinical outcome. Maintenance therapy to prevent recurrence is usually required by bone marrow transplant recipients until the recovery of adequate immune function, whereas AIDS patients may require indefinite ganciclovir maintenance therapy to prevent disease progression, as ganciclovir (like other antivirals) does not eradicate latent viral infection. Haematological effects occur relatively frequently during ganciclovir administration but are usually reversible. Ganciclovir has not been directly compared with other antiviral drugs because of the absence until recently of other effective treatments. However, comparative studies with foscarnet, particularly in cytomegalovirus retinitis, will be of considerable interest. Thus, ganciclovir represents a major advance in the therapy of severe cytomegalovirus infections in immunocompromised patients. Comparative studies, and investigation of ways of reducing toxicity (intravitreal administration; concomitant use of stimulants of haematopoiesis; use in conjunction with other antivirals with differing mechanisms of action), may further expand its eventual role.

Increased efficacy of ganciclovir in combination with foscarnet against cytomegalovirus and herpes simplex virus type 2 in vitro and in vivo

In tissue culture, efficacy against either murine CMV or HSV-2 was increased 27-fold for the acyclic nucleoside ganciclovir and 3-fold for foscarnet (trisodium phosphonoformate) when the 2 drugs were combined; whereas against human CMV, efficacy was increased 3-fold for both drugs. In mice, efficacy was increased 2-fold for ganciclovir and 4- to 5-fold for foscarnet when used in combination against either murine CMV or HSV-2. These results suggest an additive interaction between the two drugs in vivo.

Synergistic therapy by acyclovir and A1110U for mice orofacially infected with herpes simplex viruses

Clinical effects of the administration of a combination of acyclovir (ACV) and compound A1110U (a 2-acetylpyridine thiocarbonothiohydrazone inactivator of herpes simplex virus [HSV] ribonucleotide reductase) on the development of herpetic skin lesions were studied in athymic and hairless mice infected intracutaneously with different HSV type 1 (HSV-1) strains. ACV was administered topically (5%) or orally (5 mg/ml), while A1110U was applied topically (3%). In all but one experiment, the effect of combination therapy was greater than that calculated for the sum of the individual drug effects in limiting the development of herpetic skin lesions in mice. In several experiments, combination therapy totally eliminated all signs of infection. This synergistic chemotherapeutic efficacy was evident in infections caused by ACV-susceptible as well as several ACV-resistant HSV-1 strains. These results indicate that this combination therapy may provide a significant improvement in clinical responses over single-agent topical therapy.

Antiviral effects of phosphonoformate (PFA, foscarnet sodium)

This article describes the antiviral properties of foscarnet (trisodium phosphonoformate) at the enzyme level as well as in cell cultures and in vivo. The mechanism of action against herpesvirus DNA polymerases and reverse transcriptases is outlined. Clinical studies using topical foscarnet against mucocutaneous herpes simplex virus infections are presented. The clinical use of intravenous foscarnet against severe viral infections caused by cytomegalovirus, hepatitis B virus and human immunodeficiency virus is discussed.

Toxicity of intravitreal injection of foscarnet in the rabbit eye

Foscarnet (sodium phosphonoformate) is an antiviral with a high degree of efficacy against members of the herpes simplex virus family. We studied the toxicity of single doses of intravitreally administered foscarnet in the albino rabbit. Eyes were evaluated clinically and by light microscopy. Data demonstrated that doses ranging from 20 to 1000 micrograms per 0.1 milliliter are nontoxic to the retina, suggesting that foscarnet may be useful in the treatment of acute retinal necrosis and cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome.

Efficacy of 5-methoxymethyl-2'-deoxyuridine in combination with arabinosyladenine for the treatment of primary herpes simplex genital infection of mice and guinea pigs

The relative efficacy of 5-methoxymethyl-2'-deoxyuridine (MMdUrd), arabinosyladenine (ara-A) and the combination of MMdUrd and ara-A in the treatment of experimental genital herpes (GH) was investigated using mouse and guinea pig models. The infection was initiated by intravaginal inoculation using either HSV-2, strain X-265 or HSV-2, strain MS. Treatment was initiated 3 h post virus inoculation. The parameters used to evaluate efficacy were: percent mortality; mean day of death; virus yield from the vaginal secretions; and mean lesion score. The simultaneous application of 5% MMdUrd and 5% ara-A was an effective treatment for controlling primary GH in both animal models. Combination chemotherapy was also effective in preventing recurrence of infection as well as the emergence of drug resistant virus. At 20% concentration, ara-A was effective in providing protection against GH. However, lesions due to recurrent GH appeared after cessation of treatment and the virus isolated from vaginal secretions of ara-A treated animals required higher concentration of drug for inhibition of virus replication in cell culture. 20% MMdUrd was only partially effective in controlling GH. The production of infectious virus particles (virus yield) in cell culture after exposure to either ara-A of MMdUrd alone or in combination was determined. When MMdUrd and ara-A were used together, a substantially lower amount of each drug was needed to inhibit virus production completely and removal of drugs did not result in an increase in virus yield.

Mutually exclusive inhibition of herpesvirus DNA polymerase by aphidicolin, phosphonoformate, and acyclic nucleoside triphosphates

Dual inhibitor studies were performed to examine the interaction of aphidicolin, phosphonoformate, 9-(2-hydroxyethoxymethyl)guanine triphosphate, and 9-(1,3-dihydroxy-2-propoxymethyl)guanine triphosphate with herpes simplex virus DNA polymerase. Kinetic data indicated that inhibition by one agent prevents simultaneous inhibition by a second agent, producing a mutually exclusive inhibition pattern. This suggested that binding sites on the DNA polymerase molecule for these compounds are kinetically overlapping. These findings should be taken into consideration for the design of future antiviral compounds and combination chemotherapy protocols.

Resistance of herpes simplex virus to 9-[[2-hydroxy-1-(hydroxymethyl)ethoxy]methyl]guanine: physical mapping of drug synergism within the viral DNA polymerase locus

A herpes simplex virus type 2 (HSV-2) mutant TS6 (strain HG52) induces a heat-labile viral DNA polymerase at the nonpermissive temperature and is markedly resistant to 9-[[2-hydroxy-1-(hydroxymethyl)ethoxy]methyl]-guanine [2'-nor-2'-deoxyguanosine; 2'NDG]. This antiviral drug requires HSV thymidine kinase for phosphorylation to an active inhibitor (2'NDG-triphosphate), and thymidine kinase-deficient mutants of HSV exhibit varying degrees of resistance to 2'NDG, with the HSV type 1 (HSV-1) B2006 mutant (Kit) being markedly resistant. The ts6 mutation and the 2'ndgR-1 mutation within the viral DNA polymerase locus have been physically mapped by marker rescue and generation of HSV-1/HSV-2 intertypic recombinants. The physical map limits for the ts6 mutation and 2'ndgR-1 mutation are closely linked within a 2.2-kilobase-pair region of DNA sequences and are physically separate from the paaR-1 and acvR-1 mutations. Resistance to 2'NDG by HSV-2 ts6 can be overcome in the presence of combinations of 2'NDG and phosphonoacetic acid, indicating drug synergism within the viral DNA polymerase locus. These physical mapping studies expand the limits of DNA sequences defining an active center in the viral polymerase to 3.5 kilobase pairs, indicating that regions spanning the entire polymerase polypeptide may contribute to a specialized surface able to interact with nucleotides of different structure.